Headcase
by Ilovetoread09
Summary: A series of mysterious beheadings has Beckett and the team struggling to find the killer. It doesn't help that a certain writer has decided to meddle in their case. AU Collaboration with Anonymous (for now).
1. Chapter 1

AN: So here's another story I'm writing in collaboration with someone else, who wishes to remain anonymous at the moment. It's based off of the TV show Highlander. Hope you guys enjoy!

Disclaimer: We don't own Castle.

* * *

Chapter 1

 _A man walks along the streets of New York City, his hand pulling at his trench coat to keep him warm, or at least the appearance that he needs it for warmth, it's not just a fashion statement, it's hiding his most prized possession, and a deadly one at that._

 _As he walks along the street, a familiar tingling sensation begins in his spine and grows more apparent as he inches closer to home._

" _Shit," he grumbles. "Come out of hiding, whoever you are."_

" _I should have known better than to attempt to sneak up on you," a dark figure remarks from the alleyway he had just passed._

" _What do you want?" the man in coat demands, already knowing the answer._

" _Your head," the man simply replies._

 _The man on the sidewalk grumbles. "You can't have it." He slips his hand into his coat, pulling out his concealed katana, and stalking toward the man._

* * *

Detective Kate Beckett stalks toward her latest crime scene, coffee cup in hand. It's days like today where she dislikes her job. Getting up at the crack of dawn for yet another homicide with the same motive as the last four is not how she wants to start her morning.

"What do we have, Lanie?" she asks the M.E., who is currently leaning over the body.

"Another beheading, obviously," her co-worker and best friend replies, shaking her head. "Came clean off just like the other two. Looks like the same weapon was used too."

The detective purses her lips, sighing. "Any witnesses?"

Her colleague, Detective Ryan, is the one who speaks up. "Unfortunately, no. We're going to pull security footage from the camera on the corner to see if anything comes up."

"Wonder if we'll see our trenchcoat man again," Detective Esposito muses.

"Yeah, well, if we do, we're bringing him in for questioning, again," Beckett decides. For two of the prior killings, a man with a trench coat had shown up on camera near the scene. Unfortunately, the man, who went by Rick, had denied any involvement in the killings and since Beckett and her team were unable to find anything both times, they let him go. He also had solid alibis for the other two beheadings, so they were forced to cross him off the list.

"Let me know if he does come up. I want to question him myself this time." Kate figures she might be able to persuade him a little better than the boys. After all, he had asked her out when he saw her after their second failed round of questioning.

"Okay, boss," Ryan chimes and she nods, heading back to her car. She briefly glances toward the scene again before turning around and shaking her head in dismay.

Who does beheadings anymore anyway?

* * *

 _Glancing around, he gathers his bearings. A dumpster with the lid propped open, the putrid smell of rotting food seeping out into the night. A few broken bottles near a damp wall, and abandoned cardboard temple. Dark alleys are so clíche he thinks to himself, rolling his eyes and his shoulders at the same time._

" _I've been tracking some of the kills around town," The dark figure remarks, as he pulls back his hood, revealing his identity to the approaching swordsman. "Mostly newbies without mentors losing their first fight, but a couple of old-timers like you and me have bit the dust lately too." The man draws his own sword, a spatha which had served him well for many millenia. "You have anything to do with that?" The man smirks at his prey, as he brandishes his sword in an enticing manner._

" _I don't go looking for fights. I've played this game long enough to know that I don't need to," says the man in the trench coat._

" _You're right, if you play this game long enough people will come breaking down your door for your head," the figure chuckles, though the the laugh is at odds with his words, "I suppose that's the price to pay for being immortal."_

" _Let's get this over with, I'm not getting any younger here," he says with his own smile, his joke not going unnoticed by his opponent._

" _No, but I don't think you'll be getting any older either, Highlander," grins the aggressor, choosing this moment to make his first strike in an attempt to catch the other off guard._

* * *

Kate crumples up her napkin and tosses it on her desk, taking a much needed gulp of her coffee while looking at the murder board they were putting together for this new John Doe. "A beheading is weird, but a dark alley? That's just cliche," she comments, shaking her head as she sets down her coffee in lieu of a whiteboard marker.

She writes all the facts she knows about the case, which really isn't much. Not much sign of a struggle, a few broken bottles, and a broken lightbulb, but they don't appear to be related to the incident. No scuffs on the knuckles, no skin under the fingernails, the only thing wrong with the body other than it being headless was a small, round, perimortem bruise on the left temporal bone.

No wallet, no weapons found around the scene, nothing.

"Who was this guy, and why did he end up beheaded in an alley?" she muses aloud.

"Well," Detective Esposito interjects, leaning on the desk behind her, "I got these photos of the victim's tattoos from Lanie, and they're pretty unique. She said that she's never seen anything like it in person, she's only ever seen it in history books," he says, handing over the folder he's carrying.

Kate examines the artwork adorning the victim, in awe of the detail. "This stuff must have cost a fortune!" she exclaims in wonderment, flipping through the photographs. "I mean, mine-" she stops herself short.

"Your…?" Esposito prompts.

"My - uh - college roommate dropped a lot of money on a tattoo that wasn't half this good," Kate fumbles for a good cover story.

"Beckett, I've seen you naked, Chica. I know you have ink," he says in a hushed tone. "Remember that hazmat thing two years ago? Don't tell me you weren't checking anybody out!"

"Espo!" she scolds, smacking him upside the head with the stack of photos. "You may have seen me naked, but I sure as hell didn't look at you!"

"You're missing out, Chica," he hums, dancing out of her reach and shaking his butt a little from across the bullpen.

"And don't tell anyone about what you saw!" she hisses after him.

* * *

" _Ah, so you know who I am, but who are you?" the Highlander prompts as he parries the strike and spins nimbly out of the way of the next, keeping his blade in a defensive position._

" _I am Bern, the Bastard Brigand!" the man exclaims with a wild slash of his sword that catches in the Highlander's billowing coat._

" _Interesting," the Highlander comments as he uses his own blade to trap the weapon in his coat. "Did you make that up yourself, or was that what your village liked to call you as a pet name?" he teases the man, trying to rile him up._

 _The other man jerks at his sword's handle, but it won't budge. "I'd heard that you liked to cheat, Highlander," he spits._

" _Cheat? No, I would never cheat! I just like to make my own rules," the Highlander says before releasing the other blade and quickly bringing his sword hilt up and jabbing it into the other man's temple._

 _With a dazed look in his eyes, the aggressor falls to his knees, raising his sword half-heartedly in an effort to fend off any strikes._

" _You see, when people like yourself try to prey on me and attempt to take my head, I have to improvise," the Highlander sighs, readying his blade. "I wish there were another way to settle this, who does beheadings anymore anyway? They're getting too easy to track!" he says as an aside._

" _Do you normally crack this many jokes when you're about to kill someone?" Bern asks, exasperated._

" _Yes, yes I do. I'm Inigo Montoya, you killed my father, prepare to die!" he exclaims, swiftly separating head from shoulders._

" _It really is a shame that no one ever really gets to enjoy my jokes," he sighs, a weight settling on his shoulders briefly._

* * *

 _The surge of energy that surrounds him is as intoxicating as ever, and he knows how other immortals can become addicted to it, but he's unwilling to let himself succumb to such a fate. The lightning crackles all around him, sparking from an outlet in the wall, and the one working light bulb in the alley, causing it to burst. He raises his blade in the air triumphantly, conducting the energy from the Quickening, as is his ritual._

Beckett sighs, entering her apartment and swiftly closing the door. She sheds her coat in a matter of seconds and tosses it on the couch. Still no leads on the damn case and Ryan and Espo were still going through security footage when she left earlier. They had urged her to go home, saying there was nothing else to do. She reluctantly agreed, wishing she had company at home to actually compel her to return to the apartment.

She's on call tomorrow, but she doesn't need to get up early. With that in mind, she grabs a wine glass from her cabinet, filling it with her favorite wine for nights like this one. Then, she browses through her bookcase, selecting the latest in her favorite series. With satisfaction, she strolls to the bathroom and starts running the water for the tub.

She sets the two objects down onto the marble counter, strips, and steps into the porcelain tub. Grasping the book first, she opens up to the beginning page and clasps the wine glass in her free hand.

"I guess I do have company for tonight after all," she says, chuckling and allowing herself to settle into the water up to her shoulders. Shaking her head, she snorts. "It's a shame that no one ever really gets to enjoy my jokes."

So, she reads and sips, letting her body relax among the suds in the warm water, her lips curving into a small smile as she continues on, as is her ritual.

* * *

 **LIz: So, here it is. Thank you to the my fantastic friend (who wishes to remain anonymous for the moment) for collabing with me on this!**

 **Anon: Thank you, thank you … I'm sure I'll give away my secret identity EVENTUALLY!.**

 **Liz: Okay guys, we'll see you next chapter!**

 **BUT WHAT DID HE DO WITH THE WALLET AND SWORD?!**

 **\- He tossed the wallet in the river and kept the sword for his collection**


	2. Chapter 2

AN: So, here is the next chapter from my lovely partner and I. WE thank you for all the follows, favorites, and reviews for this story.

Disclaimer: We don't own Castle.

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Chapter 2

Kate Beckett strode into the precinct the next day, her body alert and ready due to a text she received from Esposito earlier that morning.

"Where is he?" she asked as soon as she stepped off the elevator.

"In interrogation 2," Ryan responded.

"Good," she said, continuing toward the interrogation room.

She took a quick peek through the one way glass of the observation room. He wore a smirk on his face, as he had the last time he was in the interrogation room. Smug bastard.

Opening the door, she greeted him, "Mr. Rodgers, it seems you're in my interrogation room, again."

"Good morning to you too, Detective," he responded, chuckling.

"You find this amusing?" She raised an eyebrow.

"C'mon, Detective, you know you don't have anything on me. Just another unfortunate circumstance."

She scoffed. "Then why are you always showing up on the street cameras near the crime scene?" She eyed him, watching as he shrugged his shoulders.

"Bad timing. And I'm sure that whatever picture you're going to show me is going to generate the same answer as last time."

"Mr. Rodgers, my patience is wearing thin. I highly suggest you tell me anything you know about these murders. Otherwise, I'll-"

"What? Arrest me? You have no real evidence. You've caught me on camera walking through the neighborhood I live in multiple times. Admit it, Detective, that's pretty thin. Obviously, you can't arrest me for being a smartass so…"

She closed her eyes, shaking her head. That man, he's so infuriating, and unfortunately, he's right.

"Look, if you really don't know anything you're free to go. However, don't forget I can have you arrested for obstruction of justice."

He rolled his eyes. "Really, Detective, I don't know anything."

Sighing, she threw the door open, gesturing for him to leave. It was early in the morning and she was not in the mood to stretch the interrogation out any longer.

As he began to walk out, he stopped in front of her, smiling.

"Now that that's over with, would you like to go out for coffee?"

Her eyes widened in surprise before turning to slits.

"No, thank you," she snipped.

No way in hell would she go out with him. It didn't matter that he was good looking or slightly charming. His attitude was a total put off, plus he's a suspect - too much conflict of interest.

"It could be fun," he replied.

She smirked, leaning closer to him. "You have no idea." She walked away, leaving him to stand in the doorway, dumbfounded.

"Yo, Beckett, how'd it go?" Esposito inquired as she returned to the bullpen.

"As well as you'd expect. Back to square one," she muttered, plopping down in her seat with resignation.

Today she was going to settle in and research the vic's tattoos and attempt to ID him. There had to be something in the tattoos, right?

She turned her computer on and began searching for the specific markings found on the victim. In the middle of it, she heard a cough come from in front of her computer. Glancing up, she scowled.

"Can I help you, Mr. Rodgers?" she grumped.

"Actually, I was thinking…"

"Is that a new thing for you?" she jabbed.

Ignoring her, he proceeded, "Since I do write murder novels for a living, I thought maybe it would be a good idea for me to consult on this case. Perhaps offer some ideas?"

She pursed her lips. "Oh? Anything I might have heard of?" she asked, taking a sip of her coffee.

" _Flowers for Your Grave_ ," he stated, shrugging.

As soon as the title left his mouth, her eyes widened to the size of saucers and she spat her coffee out all over her computer monitors and desk. This garnered the attention of several of her coworkers around the bullpen, much to her chagrin.

"You're Richard Castle?" she exclaimed, a near shout.

His eyes flashed with mirth before he shushed her for her outburst. "If you could keep it down about that, that'd be great," he spoke quietly, indicating that she should in turn.

"Why are you telling me this? Aren't you under some sort of non-disclosure agreement?" she questioned skeptically.

"That's more of a one-way street with my publisher. They can't divulge who I am without breaching our contract, but I'm free to shout it from the rooftops, should I so please," he chuckled.

"You seem like the type that would love to do that," she snarked.

"Behavior can be deceiving, Detective," he chided. "You know the old adage that you shouldn't judge a book by its cover."

She pondered that for a moment while she gathered her thoughts, and then laid down the law. "In any case, _Mr. Rodgers_ , you cannot help investigate a case in which you are a suspect."

"Not even to clear my own name?" he questioned.

She shook her head. "No, it's a conflict of interest."

He sighed, but gave her a grin. "So, does knowing my other persona change your mind?"

"About what?"

"Getting coffee with me."

She pretended to think for a minute before replying, "No." She returned to her paperwork, snickering when she heard a slight whine from the man in front of her.

"Can't blame a guy for trying," he muttered.

"It doesn't change my mind because I can't associate with suspects outside of the precinct, no matter how much I might want to."

He smirked. "So not 'no', but more 'not right now'?"

She pouted, realizing her slip up. "No comment."

Seeming satisfied with her answer, he jaunted away, waving at her before the elevator doors slipped closed.

Not that she was staring at him or anything as he left.

* * *

The following morning, Rick woke earlier than usual. He had a goal for the day, one that involved the twelfth precinct.

"If Detective Beckett doesn't want me, guess I'll have to find another way in," he mused. Really, he was disappointed she didn't want to go out with him, for now. Maybe her opinion would sway after the case was over.

"What are you doing up so early, Dad?" Alexis, his adoptive-daughter, asked.

"I plan on going to the precinct again, to pay a visit to Roy."

She furrowed her eyebrows in confusion. "The captain, right? What about?"

"I want to help with the current case, but the detective said no."

"Is this same Detective what was it...Beckett that you tried to ask out and she turned you down, twice?"

"The very same." He chuckled. Beckett's certainly different, he'd give her that. "But I really do want help. Besides, she already knows my secret and so does Roy."

Alexis blinked, shocked. "She knows you're an immortal?"

"No, the fact that I'm Richard Castle," he teased. "Sheesh, I'm not that careless."

"Did you tell her that to impress her?" she poked, snickering.

"No…" he drawled. Not really, okay, maybe a little. He'd taken a gamble when telling Beckett his profession, hoping she at least knew who he was. Throwing out his first, and most obscure, title proved that she most definitely did.

"Dad," Alexis gently scolded.

"Regardless, she didn't go for it, so it doesn't matter." He lifted his shoulders in supposed defeat. "Now, off I go. I want to get there before she does."

He headed off to the precinct, his head filled with ideas of how to approach Roy. He knew the man from a case, the one that gave him Alexis, his world.

He entered the precinct, relieved to find it mostly dead, with the exception of some uniformed officers, and of course, the captain. He knocked on the doorframe of Roy's office. The captain popped his head up, grinning as he saw Rick.

"Rick, long time no see!" the man greeted, getting up to shake the author's hand. "You look good, like you haven't aged a day." The teasing undercurrent to his statement made Rick roll his eyes in response.

"I would say the same, but I try not to lie to the authorities," Rick responded with a smirk.

"Well, headless bodies will age a man," the captain said pointedly.

"I haven't had quite the same experience. However, that is actually the reason I'm here," he shot back.

"Oh, come to make a confession?" Roy teased. "It might prevent a few more gray hairs."

"Hah. Detective Beckett putting ideas in your head?" Rick shook his head. "But no, that's not why I'm here. I think I can help. I'm pretty sure the victims are...my type."

"Oh, I thought maybe it was the Detective that was your type," Roy ribbed.

Rick nodded briefly and offered, "You're not wrong there, but I meant in more of the mythical sense, Roy."

"I know that, I've been waiting for you to come in ever since the second body dropped," Roy explained. "One is unfortunate, maybe even suspicious, but two - two indicates something a little more complex."

"Indeed," Rick mused. "Look, I need you to know, I'm not involved in most of these, and the rest - well, I think these _people_ were sent looking for me."

"So, you're the reason for all of this, technically?"

"I don't know that I'm the reason for all of it, but the ones that I've taken care of, yes." Roy raised his eyebrows. "I've been living here peacefully with Alexis for the last 15 years without running into my ilk, and now all of a sudden there's practically a mob hunting me down."

"Is it just people looking to claim whatever that prize at the end is?" Roy quizzed.

"I don't think it's that," Rick paused, stepping further into the office and closing the door behind him. "These attacks have been far too frequent and all much too overt. Our kind usually will happen upon each other and have a affable conversation before parting ways. None of these interactions could be considered nonaggressive, let alone peaceable."

"Do you think someone is sending them out to size you up? See how much you can take?"

"Could be," Rick looked out into the bullpen, watching one of the uniformed officers adjust their belt after they stood up. "It's not something that many of us have enough power or sway to do, and I can't think of a reason they would send anyone after me. I've lived a relatively low-profile existence."

"Given how old you are, I'm guessing you've pissed off some people. Is there anyone you can think of, that perhaps is still around?" Roy asked.

"Maybe one of the Riders," he said, becoming lost in thought. "Methos-" he shook his head, "No, not Methos."

"Er, who?"

"Have you ever heard of the Four Horsemen? The Riders of the Apocalypse?"

"Sure, but I don't know that much about them."

"Yes, well - they were immortals, and they did a whole lot more than anyone ever got the chance to record in a history book." His eyes clouded with grief momentarily, "but one of them, Methos - whom you may know as Death, repented, and he became a much better man. I don't think he's behind this."

"I may not have been around as long as you, but I do know that not everyone stays with their new life, repentant or not. I mean, look at junkies - they get clean for a while, and fall right back down the rabbit hole."

"Well, you don't know Methos, he's different. He's been in hiding for many years due to his distaste for the game," he explained

"If you say so," Roy muttered. "So, you want to help, huh? Let me guess, Beckett said no and now you're going over her head." The captain tsked. "You really don't want to get on her good side, do you?"

"It's not that, Roy," he hung his head. "I think I know better than most what the monsters she is after are capable of. You know too, to a degree. They won't let a detective get in their way, but they likely wouldn't risk tangoing with me, should I be there accompanying her."

The captain nodded in understanding. "So, you want to help, and maybe even protect her?"

"I can tell she wouldn't go for the protection schtick, so how about we use the guise of … book research, with a hint of expertise in bladed weapons?"

"She's not gonna like it, no matter the reason. In case you haven't noticed, she's not one for interference with her cases. However, if it stops these killings, I'll put you on the case with her. Just don't expect Beckett to be all smiles and sunshine about it."

"Great, and she was on my case about being a suspect, so we need to clear that up."

"I don't see how you could have killed anybody when we were meeting up for poker."

"Exactly," Rick commented.

Roy looked out to the bullpen, a cheshire grin forming on his face. "Speak of the devil, here she is!" He walked to the door, motioning to the detective to come into the office.

She caught sight of who was standing behind him, her eyes brightening even as her mouth transformed into a scowl. "Be right there," she called to the Captain, making a detour to her desk.

She hid her face for a moment as she stowed her bag in her desk drawer, taking an extra moment to mentally prepare herself.

Her morning ritual just got interesting.


End file.
